OF CONCHOLOGY. 193 



several Eocene shells common to the Atlantic and Pacific slopes, 

 among which is the well-known Venericardia plamcosta, Lam. 



The shells of the Isthmus Tertiary are different from Eocene 

 or Miocene shells of N. America. 



SPISSULA, Gray. 

 S. CATILLIFORMIS, Conrad. 



Description. — Suboval, inequilateral ; anterior side slightly 

 flattened or contracted ; posterior side with an oblique shallow 

 groove or fold ; lines of growth coarse and prominent; lunule 

 very long, elliptical ; ventral margin tumid posteriorly ; cardinal 

 pit oblique, large ; pallial sinus extending beyond the middle of 

 the valve. Length 4f inches ; height 3| inches. 



Inhabits Panama. 

 Spissula dolabriformis, Conrad. 



Description. — Triangular, equilateral, slightly ventricose, an- 

 terior side somewhat produced, subcuneate, rounded at the end ; 

 ventral margin regularly rounded anteriorly and medially ; 

 umbonal slope with a slight carinated line, and a distinct fold 

 anterior to it; post umbonal area with an angular groove ; epi- 

 dermis yellow olive, much wrinkled on the carinated line and 

 post-umbonal slope ; posterior end obliquely truncated, sub- 

 emarginate ; pallial sinus extends not to the middle of the valve, 

 but opposite the posterior end of the fosset. 



Inhabits Panama. 



Somewhat like 3Iactra exoleta in outline, but less elevated, 

 and not so ventricose. 



SILIQUA Muhlfeldt. 

 SiLiQUA CALiFORNiCA, Conrad. 



Description. — Oblong, equally rounded at the ends, com- 

 pressed, umbo with a broad dark violet ray ; the rib represent- 

 ing a yellowish ray distinct to the apex ; posterior to the umbonal 

 ray is a broad yellow ray which is terminated suddenly at a 

 violet concentric line ; rib oblique ; cardinal teeth diverging in 

 the right valve ; 3 in the left ; the two anterior teeth direct and 

 approximate ; pallial sinus angular at the extremity. 



Inhabits Body Bay, Calif. George Davidson. Length 1| in. 



The ray on the umbo, the more oblique rib, and especially the 

 angular sinus of the pallial line, will suffice to distinguish this 

 beautiful shell from jS'. paiula of the Sandwich Islands, 



